When struggling to keep enough funds in your account and playing the float, knowing for a certain period of time (a day or more) that any check you have written will not bounce, and therefore having some peace of mind for that period of time.

I just deposited $100 into my account, so I am "safe with the bank" until Monday.

The check for the rent will not clear until Friday, the day I am getting paid, so until then, I am safe with the bank.